Add tests that the A64FX CPU model exposes the expected features.

Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
[PMM: added commit message body]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>